Prescribed fire, snag population dynamics, and avian nest site selection

Snags are an important resource for a wide variety of organisms, including cavity-nesting birds. We documented snag attributes in a mixed-conifer forest dominated by ponderosa pine in the Sierra Nevada, California where fire is being applied during spring. A total of 328 snags were monitored before and after fire on plots burned once, burned twice, or left unburned to assess the effects of prescribed fire on snag populations. The greatest loss of snags (7.1 snags ha−1 or 43%) followed the first introduction of fire after a long fire-free period. On plots burned a second time 21% of snags (3.6 snags ha−1) were lost, whereas 8% (1.4 snags ha−1) were lost on unburned control plots in the same time period. New snags replaced many of those lost reducing the net snag losses to 12% (2.0 ha−1) for plots burned once, and 3% (0.5 ha−1) for plots burned twice and unburned plots. We also examined snags used by cavity-nesting birds. Snags preferred for nesting were generally ponderosa pine (Pinus ponderosa), larger diameter, and moderately decayed as compared to available snags. For monitored snags that met the preferred criteria, there was a net loss (1.7 snag ha−1 or 34%) after the first burn, while the loss of useable snags was less than 1 snag ha−1 following the second burn (15%) or on unburned controls (8%). We recommend protection of preferred snags, in particular large ponderosa pines, especially during primary fire applications on fire-suppressed landscapes.